Part 1:
Is there any event I can use to get a callback when the user 'change' the input field. My definition of change is to simulate the following effect. say, I want to update a label while the user typing in the input box. I tried jquery "change" event. It works, but doesn't have the live effect. Once the input field is updated, I have to click on somewhere in the screen to update the label.

Part 2:

well, if this is not a good idea, I may prevent the form being submitted on enter key. Not sure about a good way to do it either. Quick search found this answer.

<form action="" method="post" onsubmit="return false;">

not tested yet, but hopefully the submit button may still works.

EDIT: tested, and onsubmit="return false;" prevents even the submit button.